I want independence – not the UK telling me if my granny is a foreigner

So, the question facing us in Scotland, is whether, like the age of steam, our Union with England is past its sell-by date and needs to be replaced by a new relationship. Make no mistake – back in 1707, the Union was an answer of sorts to the age-old problem of fractious relations between the two countries. The Commissioners who negotiated the deal were rather more successful than their medieval predecessors, who left Anglo-Scottish relations littered with failed peace deals, broken truces and inconclusive royal marriage proposals. In 1707 Scotland got the ability to trade that it needed and England got the stability and security that it wanted. It was a deal that worked. Which is why it lasted.

Yet it was deeply flawed. It was flawed because of the older, more damaging assumption which lay behind it. Ever since Edward I came to Berwick in arms in 1296, claiming the overlordship of Scotland, the idea that England has the ultimate say in Scottish affairs has never really gone away. We see it in Henry VIII's lengthy justification for his war on Scotland, in Cromwell's arbitrary imposition of the Union, and in the repeated clauses in the Scotland Acts of 1998 and 2016 that nothing can prevent Westminster legislating for Scotland, should it so choose. British democracy has evolved in many ways since 1707, but the assumptions back then which led England to demand an incorporating Union (as opposed to the looser structure favoured by the Scots) have not really changed.

This might not matter, and arguably did not matter for much of the 19th and 20th centuries, when the Union by and large worked for Scotland's interests and little was done to antagonise relations. But that changed – with Thatcher, with an SNP government in Holyrood, with the promises made and broken after the 2014 referendum, and, most starkly, in the aftermath of the 2016 Brexit referendum when Scotland's interest, Scotland's parliament and Scotland's vote were ignored and overruled. In 2014, David Cameron promised “faster, fairer, safer and better change”. What we got were changes for the worse.

In that same speech, Cameron emphasised the British values we would retain by voting No: British values. Fairness. Freedom. Justice.

The values that say wherever you are, whoever you are, your life has dignity and worth.

The values that say we don’t walk on by when people are sick, that we don’t ask for your credit card in the hospital, that we don’t turn our backs when you get old and frail.

That we don’t turn a blind eye or a cold heart to people around the world who are desperate and crying out for help.

Where are those values now? Vanished, like snow off a dyke.

You cannot have a successful and lasting Union under these circumstances. Call it what you like – a democratic deficit – the abuse of Westminster sovereignty – the replacement of consent by force of law – the trashing of values. It boils down to the fact that the Scottish people were told one thing and got another, have no power to effect change, no matter how they vote, or how their elected representatives argue in the mother of parliaments. The idea that the Scottish people are sovereign is just so much hot air when we are faced with where the power actually lies.

And that is what independence is about. It is not about economics, nor about shared cultures, border posts, or whether your grannie is going to be a foreigner. It is about having the power to effect change without someone telling you it's not allowed, or that it's better left to others, or that you have no choice but to go along with decisions you know will be a disaster. And that power is summed up by one word: Sovereignty.

Sovereignty is the foundation of the nation state. With it, you can choose what to do; without it, you can do nothing. You can give bits of it away: all successful international treaties – the Law of the Sea, for example – involve nations giving up a bit of sovereignty for the greater good. You can use it to withdraw from the EU if you think you have given away too much. You can even use it to join a Union – such as the recently renewed Union of Belgium, Luxembourg and the Netherlands. But if you don't have it to start with, you are powerless.

Many successful democracies – such as the US or Germany – evolve ways of sharing sovereignty between the state and its component regions, and cement the contract with a constitution and a constitutional court. But not Britain. In Britain nothing can be allowed to limit the idea that the final say-so must be Westminster's. And for that, the blame lies squarely with the rule that the Westminster parliament is absolutely sovereign, can be gainsaid by no court or institution and cannot bind its successors. Those principles were laid out by Albert Venn Dicey (1835-1922), a constitutional lawyer who had no time for votes for women (“probably mentally weaker than men”), abominated Irish Home Rule, and considered the enfranchisement of black people in the US “a sham and a fraud”. Most of his views belong in a museum of outdated ideas, but his doctrine of the supremacy of parliament still persists.

Indeed, as we watch Johnson attack anything which can limit parliament, from the EU to the European Convention on Human Rights, we realise how powerful that long-dead lawyer remains, and how, like a boil on the backside of history, the divine right of kings, against which Parliament fought a war and won, has re-emerged to become the divine right of Johnson and his acolytes.

This is why none of the fine ideas about federalism or devo-max has ever come to fruition, nor ever will, and why the Sewel Convention is nothing more than words on paper. Unless a UK government chucks Dicey on the scrap-heap and thinks properly about sovereignty, nothing will change. And no UK government will seriously address the issue, because that old instinctive idea of overlordship is embedded too deep. Every time it has been challenged, by American colonists, by Irish nationalists, by Gandhi's Out of India movement, even by Europe's “ever-closer union”, the reaction has been the same: insist on retaining sovereignty, deploy spurious arguments, threaten force if need be, resist all compromise until damage has been done to both sides, and give way only when there's no alternative.

It's not as though a different way of doing things hasn't been thought about. Back in 1983, when the need for devolution was still a hot topic, Jo Grimond, former leader of the Liberal party, wrote: I do not like the word devolution as it has come to be called. It implies that power rests at Westminster, from which centre some may be graciously devolved. I would rather begin by assuming that power should rest with the people who entrust it to their representatives to discharge the essential tasks of government. Once we accept that the Scots and the Welsh are nations, then we must accord them parliaments which have all the normal powers of government, except for those that they delegate to the United Kingdom government or the EEC.

That was (and remains) the most pragmatic way to reconstruct relations within the British Isles. But it is incompatible with undiluted Westminster sovereignty, and so even Jo Grimond's former party has turned its back on it, to its lasting detriment.

It's only a small step forward from this to realise that Scottish independence is the best, maybe the only, way of forcing the remains of the British state to re-examine itself. Those who regard with horror the untrammelled ability of Johnson to override all the unspoken checks and balances on which the unwritten constitution supposedly depends should reflect on this. The conditions which brought Johnson to power were not created overnight, but are the product of 300 years of exceptionalism and inflexibility. Through an independent Scotland rejecting this, the decay at the heart of the Union will finally be exposed, and the opportunity will be there to create something different and better.

What might that look like? No one is suggesting that an independent Scotland could sail off into the blue and ignore its neighbour. And no matter how much irritated Brexiteers down South call for the rebuilding of Hadrian's Wall, that is not a solution either. The relationship needs to be re-forged, especially because you don't go through 300 years of a Union without having built much of value – not least the myriad family ties and the many shared cultural connections. These will need to be preserved along with many of the more mundane pieces of shared infrastructure and institutions, which there is no need to tear up overnight.

We need to consider how to manage that – how to retain the remaining better parts of Britishness while rejecting the accumulated dross. We need to hold out reassurance to our own people, and to those in England and Wales, who still have a nostalgic attachment to the Union. Taking the “loser's dividend” seriously – as the hard Brexit advocates never did – is the best way of avoiding a lasting resentment and sadness among those who will, despite everything, still vote No to independence. So we need to do the work, and get the offer on the table – because one thing we should learn from Vote Leave is that a superficially attractive campaign that does not think through the consequences and is based on false promises leads to a very bad place.

Effectively, everything is on the table to be negotiated. At one end, a possible time-limited treaty of confederation, with sovereign nations agreeing what they will do together through a supra-national body; at the other a much looser series of bilateral agreements. Division of assets and liabilities to be sorted out; the status of citizens and their cross-border rights to be agreed. There's nothing to be frightened of – it's been done before. Plenty of countries, particularly since the break-up of the Soviet Union, have gone through the process and emerged as successful independent nations. Ask the Slovenes, or the Estonians.

But to negotiate a new relationship you first need the power to negotiate. And if you don't have that power because you don't have sovereignty, then you need independence. Because being independent is the only thing that unquestionably gives you sovereignty. That is why Scotland needs independence and why nothing else will do.

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